Characterization of porous poly-silicon as a gas sensor

Porous poly-silicon (PPS) is a cheaper alternative to single crystal porous silicon and is a favorable choice for making gas sensors. In this study, porous poly-silicon samples were prepared using different HF concentrations and the structural and gas-sensing properties were studied. The topography of the surface was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The variation of electrical conductivity of the samples in the presence of dry air-diluted acetone, ethanol and methanol showed that for a constant etching current, the sensitivity was highest for samples prepared in 13% HF solution. The structure of the films in the optimum HF concentration is micrometer-sized islands with nanopores inside. The I–V curve varies in the presence of ethanol when the tip of STM is positioned on the islands. It was revealed that the sensitivity of samples annealed in air and samples boiled in CCl₄ decrease strongly. XPS data showed that the surface of the sample after boiling in CCl₄ is partially oxidized.